The DVB standard for broadcasting over-the-air video signals (e.g. video/television) is used in many countries as the present method for transmission of digital television signals. The DVB standards include standards for cable transmission (“DVB-C”), satellite transmission (“DVB-S”), over-the-air terrestrial transmission (“DVB-T”), and recently, specific DVB-T transmission to mobile devices (“DVB-H”). The DVB-T standard supports the transmission of standard definition (“SD”) and high definition (“HD”) video and data signals to receivers such as HD-ready televisions, and more frequently, set-top boxes (“STBs”) that receive the signals from transmitters and provide digital, or analog, television compatible outputs for viewing.
FIG. 1 depicts a simplified block diagram for a typical DVB application. In FIG. 1, a DVB transmission system provides an MPEG multiplexer 3 that combines MPEG-2 broadcast streams of video, audio, and/or data content, these MPEG-2 streams output from the MPEG-2 multiplexer 3 are then input into a transport stream multiplexer 5 having multiple inputs, the output of this transport stream multiplexer, transport stream (“TS”) signals, are then signal modulated by modulator 7 for DVB-T transmission including OFDM, guard interval (“GI”) insertion, and then processed to radio frequency (“RF”) signals using an analog transmitter 9 including a digital-to-analog converter (“DAC”) and an analog front end (“AFE”). These RF DVB-T signals are then transmitted over the air using an antenna 11. As is known to those skilled in the art, insertion of guard intervals or GI for OFDM symbols, where the “tail” of the symbol is repeated in front of the symbol for a time period, can be used to eliminate problems caused by the inter-symbol interference (“ISI”). ISI is often caused by multipath reception (receiving multiple copies of the same transmission) at the receiver. These GI symbols are later removed at the receiver.
On the receiving end, DVB capable television receivers 23, or alternatively set top boxes 15, receive the RF signals from antennas 21 and 13, respectively. The RF signals received are then processed back to digital signals in MPEG-2 format using an analog front end (“AFE”) and analog-to-digital converter (“ADC”), and the signals are then demodulated, demultiplexed and the receiver then provides a selection of video and audio signals to a television or video monitor, for viewing by the user. Some recently produced televisions or monitors such as 23 shown in FIG. 1 may include integral DVB receivers. Users may also receive DVB-T signals using a set top box or dedicated receiver equipment, such as 15 in FIG. 1, and receive an output on an analog television such as 17 in FIG. 1. The television 23 with an integrated DVB-T receiver capability may eliminate the need for a set top box. In some environments the set top box may include additional desirable functionality, such as digital video recording (“DVR”) that the user may use to capture video streams for viewing at a time different than the broadcast time. In any event, once the DVB signal is received, the user can select from the variety of digital video streams and view them.
As handheld devices for wireless communication systems such as cellular telephones, media players, and personal digital assistants (“PDAs”) become widely deployed and continue to attract a growing number of users, there is a commercial need to provide video signals, such as television broadcasts, to mobile or handheld portable devices. The DVB-H standard adds certain features to the basic DVB-T standard specifically directed as such receivers. In FIG. 1, a handheld video receiver 19 is shown. Additional DVB standards provide the capability for a user to send responses to the transmitter via a “return channel,” so that the mobile device is more than a receiver and may also provide interactive services such as email, text messaging, internet browsing and the like.
DVB-T broadcasting is based on an orthogonal frequency division multiplexed (“OFDM”) modulation signaling scheme. This modulation provides a robust signal and a large number of sub-carriers. The DVB-T scheme provides additional features: options that a broadcaster might use are one of three modulation types: quadrature phase shift keying (“QPSK”), 16QAM, 64QAM, one of five different forward error correction (“FEC”) rates, one of four different GI lengths, a choice of carriers (2K, or 8K) and a choice of channel bandwidths (6, 7 or 8 MHz). DVB-T can support services such as standard definition digital TV (“SDTV”), high definition digital TV (“HDTV”), radio, interactive services (with return channels) and IP data casting (supporting, for example, internet browsing). DVB-T also features hierarchical modulation, which provides a high priority (“HP”) and a low priority (“LP”) transport stream. Two different services may be simultaneously broadcast for different receivers, for example, standard definition (“SD”) and high definition (“HD”) broadcasts.
The robustness of DVB-T has proven capabilities for mobile devices. The DVB-T standard has been improved further with specific standardization directed at mobile receivers in the DVB-H standard. DVB-H adds to DVB-T additional features directed at optimizing broadcasts for mobile receivers, including time slicing, or bursty transmission, which allows the mobile to save power (especially important for battery operated devices); additional modes such as a 4k mode, a compromise between mobile reception capability and SFN cell size; additional forward error correction code MPE-FEC; and an in-depth interleaver which is a short time interleaver for 2k and 4k modes.
Currently, many countries are transitioning from a broadcast environment that includes both DVB-T and pre-existing UHF/VHF analog television over-the-air broadcasting as signals in the frequency spectrum available for television. These transitions are presently moving to an environment of purely digital video broadcasting, over a time period known as “analog turn off.” At that time, additional frequency spectrum for digital video broadcast transmissions will become available. In order to further enhance DVB broadcasting and to take advantage of this additional available broadcast spectrum, efforts are presently underway to extend DVB-T standards to next generation (sometimes referred to as “second generation” or “2G”) digital video broadcast standards. These standards are presently referred to using various acronyms, but often are referred to as “DVB-T2” for the next generation terrestrial DVB standard, and “DVB-H2” or “DVB-NGH” for the next generation handheld device or mobile DVB standard. Goals for extending the DVB terrestrial standards to the new DVB-T2 standards include increasing higher payloads, providing optimum reception for fixed and mobile receivers, adding additional carriers, reducing peak power, adding multiple-input multiple-output diversity antennas, and better support for internet protocol (“IP”) data streaming. New methods and devices for receiving and processing these next generation DVB signals, in an efficient, economic and robust manner, using approaches compatible with existing integrated circuit and receiver technology, without adding significant costs to systems or to the end consumer, are desirable.